Impregnant compositions for porous articles

ABSTRACT

The sealing of small porous rigid articles by impregnation with a liquid synthetic resin impregnant and sequent curing of resin in the pores and provides a liquid (meth)acrylic ester impregnant composition comprising a free radical catalyst, an inhibitor and a higher alkyl (meth)acrylic ester and/or polyfunctional (meth)acrylic ester which has been obtained by transesterification in the presence of an organotitanium catalyst and from which the catalyst residue has not been removed. The catalyst residue has been found to improve sealing and thermal stability of the cured impregnant.

The invention relates to the sealing of small pores in porous rigidarticles by impregnation with a liquid synthetic resin impregnant andsubsequent curing of resin in the pores. The articles includeparticularly metal castings and sintered metal parts but also includematerials such as wood or inorganic materials such as brick, stone orconcrete.

The impregnation of metal castings with resins to seal porosity is aprocess which is well established. Porosity in castings is invariablyinconsistent in size and shape, thus rendering the components unusabledue to leakage. This is especially true where they are subjected topressure. Apart from this well known cause for rejection of castingsused in the motor industry there are many other problems caused byporosity including plating failures, "blow out" during stove enamelling,and sites for corrosion, entrapment of organic material and possiblebacteria growth.

Generally, porosity can be divided into three types: through porosity,blind porosity and enclosed porosity. Through porosity causes leakageand is the type with which founders are primarily concerned. Blindporosity, having one entrance to the surface only, will not produce aleakage but can cause surface finishing problems through absorption oftreatment fluids. Enclosed porosity causes no problems unless present inexcess where it can cause structure failure. Other similar defects oftenencountered in the foundry include cold laps, cracks, blow holes, andinclusions all of which are often referred to, incorrectly, as forms ofporosity. Frequently examination of a casting rejected for leakage andmarked by the inspector as porous, reveals that it actually has a coldlap, crack or a blow hole.

Various methods of sealing porosity employed over the years includeplugging, coating with epoxy resin, and welding. All of these techniquesare highly labour intensive and therefore expensive, and there is noguarantee that the treatment will be successful.

One preferred impregnation technique for sealing porous articlescomprises immersing the article in liquid impregnant under vacuumconditions in an autoclave, allowing the pressure to rise so forcing theimpregnant into the pores, removing the impregnated article, washing theimpregnant from the surface and curing the impregnant which remains inthe pores. The article is preferably subjected to vacuum conditionsbefore immersion in the liquid impregnant but it is also possible toimmerse the article in the impregnant before drawing the vacuum in theautoclave. The washing step is desirably carried out using water and inmany cases it will be desirable to include a surfactant either in thewater or in the impregnant. The impregnants normally used are based onone or more esters of (meth)acrylic acid, at least some of esters beingderived from polyfunctional alcohols in order to provide cross linkingon curing. The impregnant will normally contain a free radical-producingcuring agent such as a peroxide or azo compound and an inhibitor such asa sterically hindered phenolic compound. It is also desirable to includea small amount of metal chelating agent. Compositions catalysed byperoxy compounds and azo compounds can be heat-cured e.g. by immersingthe article in hot water at say 90° C. Anaerobically curing compositionson the other hand require peroxy catalysts.

The impregnant compositions should have a sufficiently low viscosity topermit them to be drawn into the pores of the article (it should benoted in this connection that metal castings tend to have smaller poresthan sintered metal articles). On the other hand, too low a viscosityencourages unwanted leaching out of impregnant from the pores during thewashing step. Also, of course, water solubility has to be taken intoaccount if an aqueous wash liquid is used. Furthermore, impregnants oflow volatility clearly have to be used in order to avoid boiling offunder vacuum conditions. A low surface tension liquid impregnant is alsodesirable since it permits wetting of the metal in the pores andimproves adhesion of the cured resin.

The storage and curing properties of the impregnant composition can beappropriately adjusted by varying the proportions of the catalyst andthe inhibitor. My U.K. Patent No. 1,547,801 describes variouscompositions which are stable at room temperature and which may be curedat 90° C. in a water bath in a period from 3 to 15 minutes. Furthercompositions of this type are disclosed in European Patent No. 14062 ofLoctite (Ireland) Limited. Anaerobically curing systems are for exampledescribed in UK Patent No. 1,527,448 of Loctite Corporation. Thesedocuments describe examples of impregnant compositions of the type withwhich the present invention is concerned and give examples of monomers,catalysts and inhibitors together with the proportions in which they maybe used.

As further background prior art, it should be mentioned that JapanesePatent Application No. 56-130182 (Kokai No. 58-32612) of Chuo HatsumeiKenkyusho K. K. describes an impregnant based on (meth)acrylic esters. A"titanium coupling agent" may be included for lowering the surfacetension and improving adhesion to metal, but no examples of suchcoupling agents are given.

According to a principal aspect of the present invention, there isprovided a liquid (meth)acrylic ester impregnant composition comprisinga free radical catalyst, an inhibitor and a higher alkyl and/orpolyfunctional (meth)acrylic ester which has been obtained bytransesterification in the presence of an organotitanium catalyst andfrom which the catalyst residue has not been removed. The composition ispreferably room temperature-stable (without aeration) and hotwater-curable and the preferred transesterification catalyst istetra-isopropyl titanate. While impregnants of the invention willnormally be sold with the free radical catalyst mixed in, it isenvisaged that the catalyst may be supplied in a separate pack foraddition by the customer.

According to a second aspect of the invention there is thereforeprovided a liquid (meth)acrylic ester impregnant composition comprisinga hydroxyalkyl (meth)acrylate, a higher alkyl (meth)acrylate and apolyfunctional (meth)acrylate, at least one of the higher alkyl orpolyfunctional (meth)acrylic ester being a (meth)acrylic ester which hasbeen obtained by transesterification in the presence of anorganotitanium catalyst and from which the catalyst residue has not beenremoved.

According to another aspect of the invention, there is provided aprocess for preparing a liquid (meth)acrylic ester impregnantcomposition which comprises reacting a lower alkyl (meth)acrylate with ahigher alcohol in the presence of an organotitanium catalyst to providea higher alkyl (meth)acrylate, and adding a polyfunctional(meth)acrylate and/or a hydroxyalkyl (meth)acrylate to the reactionproduct without removal of the organotitanium catalyst.

According to a further aspect of the invention, there is provided aprocess for preparing a liquid (meth)acrylate ester impregnantcomposition which comprises reacting a lower alkyl (meth)acrylate with apolyfunctional alcohol, such as a glycol or a polyalkylene glycol, inthe presence of an organotitanium catalyst to provide a polyfunctional(meth)acrylate and adding a higher alkyl (meth)acrylate and/or ahydroxyalkyl (meth)acrylate to the reaction product without removal ofthe organotitanium catalyst.

The most preferred impregnant compositions with which the invention isconcerned include as polyfunctional (meth)acrylate, polyethylene glycoldimethacrylate, triethylene glycol dimethacrylate, trimethylol propanetrimethacrylate and tetraethylene glycol dimethacrylate. As explained inU.K. Patent No. 1,547,801, it is, however, desirable to include somemonofunctional (meth)acrylate because the monofunctional compounds aremore stable and less susceptible to anaerobic effects. Furthermore,wholly polyfunctional (meth)acrylate esters tend to shrink on curing toa greater extent than mixtures with monofunctional esters which can leadto leakage problems. Polyfunctional (meth)acrylate ester resins are alsomore brittle so that a plasticising effect is necessary to give thenecessary properties; the plasticising effect may be obtained byincorporating a conventional resin plasticiser such as dioctyl phthalateor it may be obtained by using a monofunctional (meth)acrylatecomonomer. Lower e.g. C₁ to C₃ monofunctional (meth)acrylates such asmethyl (meth)acrylate tend to be too volatile and C₁₀ to C₁₄ alkyl(meth)acrylates are more preferred. It is also desirable to include ahydrophilic alkyl (meth)acrylate such as hydroxypropyl methacrylate orhydroxyethyl acrylate to facilitate washing and to improve adhesion ofthe cured resin.

Among suitable monofunctional esters are those having the formula:

    CH.sub.2 ═C(R.sub.1)COOR.sub.2

where R₁ is H or CH₃, R₂ is C_(n) H_(2n+1) or C_(m) H_(2m) OH (where nis 4-18, preferably 4-14, particularly 10-14 and m has similar valuesexcept that the minimum value can be as low as 2), CH₂ CH₂ O(CH₂ CH₂O)_(x) H or CH₂ CH(CH₃)0(CH₂ CH₂ (CH₃)0)_(x) H, where x is 0 to 10 (theunits optionally being reversed in the case of propylene glycol). Asexamples, butyl acrylate, hydroxypropyl acrylate, 2-ethyl-hexylacrylate, lauryl methacrylate, tridecyl methacrylate and stearylmethacrylate may be cited. Although many monoesters of acrylic and/ormethacrylic acid may be employed, the actual choice will be governed onthe one hand by avoidance of too high a volatility and on the other bythe desirability of a low viscosity. At least sufficient polyfunctionalmonomer should also be present in order to provide a cross-linked resinon curing.

The proportion of polyfunctional (meth)acrylate ester monomer may varydepending on the degree of solvent and heat resistance expected of thesealed article but is desirably in the range 2-70% of the impregnant andpreferably lies in the range 2-40% most preferably 5-25%. The upperlimit is determined in part by economic considerations as thepolyfunctional esters are more expensive. More important is the factthat monofunctional acrylates or methacrylates appear to be more stableand less susceptible to anaerobic effects than polyfunctional monomers.It is a feature of the preferred process that curing takes place in hotwater even in the presence of some dissolved air. Systems which exhibittoo great an anaerobic effect can cause difficulties with certainparticularly active metal alloys. In extreme cases of anaerobic systems,particularly where a sintered component is involved, a thin film ofpartially cured resin is already present on removal from the autoclaveand this is difficult to remove by washing and results in dirtyproducts.

Although the preferred impregnants are substantially wholly(meth)acrylate ester (at least as far as the monomers are concerned),other monomers such as diallyl phthalate or esters based on maleates orfumarates may also be included in small quantities, as maynon-polymerisable extenders such as phthalate esters e.g. dibutylphthalate or dioctyl phthalate. Too high a proportion of extender shouldbe avoided as castings in contact with solvents may developmicroporosity due to migration of the extender.

It may be convenient to include surfactants (which term includesemulsifying agents, wetting agents and detergents) in the impregnant asan aid to subsequent water washing. The choice of surfactant will bebased on the usual principles and will be determined by the actualcomposition of the impregnant. In general the most useful surfactantswill be found amongst those recommended for use with liquids of highpolarity rather than those designed for emulsification of paraffinicoils. Although cationic and anionic surfactants can be used, non-ionicsurfactants of the ethoxylated and propoxylated alcohol type arepreferred, e.g. at 0.1 to 1% concentration if added to the wash water or1 to 10% if present in the impregnant. Sodium metasilicate at a level ofabout 1% has been found to be effective in the wash water.

Many catalysts and inhibitors have been found satisfactory for theoperation of the preferred impregnation process. The principle governingthe choice is that the combination should desirably give rise to animpregnant, a sample of which when placed in a test tube at 90° C.should gel in a time of between 1 to 15 minutes and preferably 1.5 to 5minutes. Typically the quantities may be selected within the range0.1-15%, preferably 1-5% catalyst and 0.01-2% inhibitor. A wide range ofcatalysts including benzoyl peroxide, methyl ethyl ketone peroxide,various alkyl peresters, cumene hydroperoxide and azo catalysts such asAZBN (azobisisobutyronitrile) have been found suitable. A similarly wideselection of inhibitors has been found suitable, including those incommon use such as hydroquinone, substituted hydroquinones such asmethoxyhydroquinone, p-cresol and m-cresol, and various hindered alkylphenols such as 2,6-di-tert-butyl p-cresol and 2,5-di-tert-butylhydroquinone; methylene blue is also useful. The viscosity of such animpregnant has been found to remain almost constant when the throughputof castings is such that there is a residence time for the impregnant inthe autoclave of several weeks.

Various metal ion chelators of the type described in European Patent No.14062 may also be included in the impregnant.

The time required for impregnation varies with the type of product. Inpractice a time of 10 minutes at a vacuum of 2-5 mm of Hg has been foundsufficient for the majority of commercially available castings. In thecase of one small sintered iron component 3 minutes was found sufficientwhereas in another instance impregnation of wood was found to require 30minutes. In no instance was pressure required.

Various methods of conveying the articles through the stages of theprocess may be used. Generally it is found convenient to pack mediumsized castings in baskets constructed of steel mesh. Thus on removalfrom the impregnant, the basket can be drained over a draining tray andit is advantageous if the angle of tilt of the baskets can be altered toallow more thorough draining.

Immersion of the articles in a water or water plus detergent tank allowsimpregnant to be worked from the surface within 10 minutes. Agitationshould be provided to facilitate this process. The use of water as awashing medium is both economical and safer than the use of solvents.One of the greatest deterrents to widespread use of impregnationequipment is connected with effluent disposal problems. It is a featureof the process that apart from the methods available to break emulsionswhich will be familiar to those accustomed to dealing with the disposalof cutting oils, a simpler method has been found possible. Thus when thelevel of emulsified impregnant has built up to a concentration of 1-5%,the wash liquors may be pumped to a separate tank capable of raising thetemperature above 80° C. For example after only 2 minutes at 100° C.,the emulsion suddenly curdles and on cooling, the nearly clearsupernatent liquid may be drained into the sewer leaving a damp granularsolid which, being a polymer, may be disposed of as an inoffensivealmost odourless solid waste. At 90° C. curdling may take 20 minutes.

Following rinsing, the articles are drained for a few moments and thentransferred to the curing tank. The use of hot water to cure theimpregnant offers several advantages over other alternative procedures.The hot water acts as an additional washing medium to remove traces ofpartially emulsified impregnant from the surface of the casting,particularly from the inside of tapped holes. It is commonly found thatprocesses employing oven curing result in dirty castings and thisimposes limitations on the type of casting which may be sealed by thismethod. Another advantage in curing in hot water arises from the factthat, as is well known, many monomers of which methacrylates and styreneare examples are inhibited by air and consequently satisfactory curingof resin takes place even at the surface of the pores where the wateracts as a barrier. With low viscosity impregnants there is obviously arisk that hot oils or solvents might leach impregnant from the largerpores before curing could take place. The use of hot water has beenfound to be satisfactory in this respect. Thus plating processes, to besuccessful, require that the level of resin in the pores should be suchthat entrapment of plating fluids beneath the metal plating is avoided.Satisfactory plating of sintered parts has been shown to be possibleusing the process of the invention. It is also convenient that onremoval of castings from the hot water almost immediate evaporation ofwater occurs and when cool, the castings are immediately ready forpressure testing or any further engineering operations.

The temperature of the water in the curing tank should be such that anadequate margin exists for curing the monomer in the time allotted forimmersion. In a preferred embodiment of the invention the impregnantwill have a curing time at 90° C. of 10-15 minutes. It will be clearthat at temperatures above 95° C. the presence of steam will becomeincreasingly inconvenient. Below 70° C., the required immersion time toensure satisfactory curing lengthens considerably unless thecatalyst/inhibitor balance is altered. However this implies that thestability of the impregnant in the autoclave is reduced. It is thereforedesirable that the curing temperature should be in the range 80° C.-95°C. and preferably close to 90° C.

A feature of the preferred process is therefore that although severalstages are involved, none require longer than 10 minutes and this allowsa sequence of baskets containing castings to be processed in anunusually compact design of plant.

Although vacuum impregnation is the preferred method of carrying out theprocess, pressure impregnation could be used or indeed the article couldsimply be dipped into the impregnant.

Higher alkyl (meth)acrylates and polyfunctional (meth)acrylates arenormally manufactured in practice by a transesterification, or morecorrectly alcoholysis, reaction, between methyl (meth)acrylate, asuitable higher alcohol and a catalyst in a suitable proportion foreffecting the reaction within a suitable time at a convenienttemperature. As mentioned above, the higher alkyl (meth)acrylates usefulfor the present invention are generally C₄ -C₁₈ alkyl, preferably C₄-C₁₄ alkyl and particularly C₁₀ -C₁₄ alkyl.

The higher alcohol reacts with the methyl (meth)acrylate at temperaturesaround 100° C. (50°-150° C.) to produce higher alkyl (meth)acrylate andmethanol, the latter being removed from the reaction zone in order todrive the reaction to completion. The alcoholysis reaction will often becarried out using a stoichiometric excess of methyl (meth)acrylate toensure complete conversion of higher alcohol to ester. It is also commonpractice to include a hydrocarbon solvent such as cyclohexane or benzenein the reaction mixture to facilitate the separation and removal of theby-product methanol from the methyl (meth)acrylate reactant via anazeotropic distillation. Inhibitors, such as substituted phenols orother inhibitors, will also be included to prevent prematurepolymerisation of the monomers during the reaction.

Upon completion of the reaction, indicated by cessation of methanolevolution, it is usual to purify the products prior to use first byremoving any volatile materials such as excess methyl (meth)acrylate bydistillation under vacuum and then to vacuum distil the product itself.Should the product have such a high boiling point as to renderdistillation difficult or impossible without polymerisation the productwould be purified by treatment in the liquid state to adsorb and removecatalyst residues or coloured bodies etc.

Treatment can also take a form whereby catalyst residues are reacted,e.g. by alkaline hydrolysis, to render them insoluble so that theyprecipitate from the product and can be removed by a suitable means suchas filtration, centrifugation, or adsorption onto charcoal prior tofiltration. Such purification stages are both time consuming and lead toyield losses and therefore add significantly to the cost ofmanufacturing higher alkyl (meth)acrylates and polyfunctional(meth)acrylates.

We have now found, according to the invention, that it is not necessaryto remove the catalyst, and that the higher alkyl or polyfunctional(meth)acrylate can be used in the condition that appertains afterreaction and removal of by-products such as excess methyl (meth)acrylateand methanol. The use of higher alkyl and polyfunctional (meth)acrylateswithout removal of the catalyst in an impregnant composition lowers thesurface tension of the composition leading to improved wetting andadhesion. Cured impregnants also show greater stability when subjectedto elevated temperature conditions such as 200° C. The omission of thestep of removing the catalyst also reduces the cost of producing theimpregnant composition.

The catalyst normally used for the alcoholysis transesterificationprocess is an organometallic titanium compound, particularly a tetralower alkyl orthotitanate such as tetra isopropyl titanate ortetra-n-butyl titanate, or the titanate of the relevant higher alcoholcould also be used. Titanates are effective transesterificationcatalysts as they do not promote side reactions and only requiremoderate temperatures.

Thus according to a further aspect of the invention there is provided aliquid (meth)acrylic ester impregnant composition for porous articlescomprising an organometallic titanium compound which is preferablysoluble therein, preferably a tetra alkyl orthotitanate or the titaniumcompound derived therefrom during the course of transesterification. Inthis connection, it has been found that adding a similar amount oftitanium catalyst to an impregnant composition made from purifiedmonomers from which the original catalyst has been removed is generallyless satisfactory e.g. because the added titanium compound tends toprecipitate out. It is now believed that the catalyst residue normallyremoved from the transesterification product is the tetra-alkoxidederived from the higher alkyl group or the polyfunctional alkyl groupand not the original catalyst (which is more susceptible to hydrolysis).It is also believed that hydroxyalkyl (meth)acrylate esters may play apart in binding the catalyst residue.

It is accordingly within the ambit of the invention, though much lesspreferred, to add an organotitanium compound such as a higher alkyltitanate, to a purified monomer system.

According to yet another aspect, the invention provides a process forpreparing a liquid (meth)acrylate ester impregnant composition whichcomprises reacting a lower alkyl (meth)acrylate with a higher alcoholand a polyfunctional alcohol or a mixture thereof, either alone ortogether, in the presence of an organo titanium catalyst to provide amixed (meth)acrylate ester composition and adding one or more otherdesirable (meth)acrylate esters such as hydroxyalkyl (meth)acrylates,polyalkylene glycol mono(meth)acrylates, (meth)acrylate containingoligomers etc.

Our experiments have shown that it is desirable for the impregnant tocontain at least 50, preferably 100-1000, ppm Ti derived from thetransesterification catalyst.

EXAMPLES

A range of impregnation compositions (sealants) was prepared usingmonomers prepared and purified to a normal commercial quality and alsomonomers according to this invention in which the tetra-isopropyltitanate esterification catalyst was allowed to remain in the monomer.These sealants were subjected to a series of evaluation tests asdetailed below.

Sealing Performance

Annular sintered iron test rings of 20% pore volume and dimensions 25 mmoutside diameter, 14 mm inside diameter, and 14 mm height wereimpregnated using a wet vacuum technique. This consisted of immersingthe rings in the sealant and subjecting them to vacuum of 5 mbar for 10minutes to remove air from the porosity, and releasing the vacuum toatmospheric pressure to fill the pores with sealant. The rings wereremoved from the sealant, allowed to drain, washed with water and thesealant polymerised in the pores by immersing the rings in hot water at90° C. for 10 minutes. The rings were pressure tested under water withair at 90 `psi` pressure and assessed for leaks on a 0-5 scale with 0signifying no leakage and 5 a level of leakage at which castings (asopposed to tests rings) might not be 100% sealed.

Thermal Stability

Small samples of sealant were polymerised in 3 mm diameter test-tubesfor 30 minutes at 90° C. The samples were removed from the test-tubesand the percentage loss in weight determined after 1 hour and 24 hours,at 150° C. and 200° C. The percentage loss in sealant weight was alsodetermined under the same conditions but using impregnated sinteredmetal test rings as described above.

Gel Time

A 5 ml sample of sealant was heated in a test-tube in a water bath at90° C. The time taken for polymerisation to proceed to a point where thetube and its contents could be lifted from the water bath on the end ofa piece of wire immersed in the sealant was determined.

The following three sealant formulations were prepared with the amountsbeing given in parts by weight.

    ______________________________________                                                           1    2      3                                              ______________________________________                                        Hydroxypropyl methacrylate                                                                         65     65     65                                         Lauryl methacrylate  15     --     --                                         Lauryl methacrylate (inc.                                                                          --     15     15                                         catalyst residue 600 ppm as Ti)                                               Triethylene glycol dimethacrylate                                                                  20     20     --                                         Triethylene glycol dimethacrylate                                                                  --     --     20                                         (inc. catalyst residue 1000 ppm as Ti)                                        Azobisisobutyronitrile                                                                             0.4    0.4    0.4                                        Inhibitor (sterically hindered                                                                     0.15   0.15   0.15                                       substituted phenol)                                                           Residual Ti in ppm (based on whole                                                                 0      90     290                                        formulation)                                                                  ______________________________________                                    

Results of the various tests are given in the table below:

    ______________________________________                                                       1        2      3                                              ______________________________________                                        Gel time @ 90° C. Min                                                                   1.25       1.0    1.2                                        % Wt loss at 200° C.                                                   Test piece                                                                              (1) 1 Hr   3.2        3.3  1.7                                                (2) 24 Hrs 51         32   9.0                                      Test Ring (1) 1 Hr   7.4        5.1  6.3                                                (2) 24 Hrs 56         26   21                                       Test Ring Sealing Rating:                                                     After polymerisation                                                                           3          2      0                                          After 1 Hr @ 150° C.                                                                     3+        3      0                                          After 24 Hrs @ 150° C.                                                                  4          4      0                                          After 1 Hr @ 200° C.                                                                    5          4      0                                          After 24 Hrs @ 200° C.                                                                   5+         4+    0                                          ______________________________________                                    

The results quoted are the average of duplicate tests and they clearlyindicate the superior sealing performance and improved thermal stabilityof the sealants of the invention.

The following five sealant formulations were prepared with the amountsbeing given in parts by weight.

    ______________________________________                                                      4     5      6      7    8                                      ______________________________________                                        Hydroxypropyl methacrylate                                                                    25      25     25   25   25                                   Tridecyl methacrylate                                                                         70      52.5   35   17.5 --                                   (purified)                                                                    Tridecyl methacrylate                                                                         --      17.5   35   52.5 70                                   (including catalyst                                                           residue 150 ppm as Ti)                                                        Trimethylolpropane                                                                            5       5      5    5    5                                    Trimethacrylate                                                               Azobisobutyronitrile                                                                          0.4     0.4    0.4  0.4  0.4                                  Inhibitor (sterically                                                                         0.15    0.15   0.15 0.15 0.15                                 hindered substituted                                                          phenol)                                                                       Residual Ti in ppm                                                                            0       26     52.5 79   105                                  % Wt loss at 200° C.                                                   Test piece                                                                            1 hour      6.3     2.8  3.2  3.4  3.0                                        24 hours    63.4    43.0 16.3 17.6 16.3                               Test ring                                                                             1 hour      4.9     6.5  7.1  6.4  4.1                                        24 hours    29.6    29.5 27.5 24.2 25.5                               Test ring sealing rating                                                      After polymerisation                                                                          0       0      0    0    0                                    After 1 hour at 200° C.                                                                1       0      0    0    0                                    After 24 hours at 200° C.                                                              1       2      0    0    0                                    ______________________________________                                    

It will be apparent from the Formulations 4-8 that good sealing isachieved and this is primarily attributable to the high proportion oftridecyl methacrylate which gives flexibility to the cured product. The5% polyfunctional methacrylate is in fact sufficient to make the resinthermosetting. On the other hand the presence of Ti increases thermalstability markedly.

I claim:
 1. A liquid (meth)acrylic ester impregnant compositioncomprising a free radical catalyst, an inhibitor and a higher alkyl(meth)acrylic ester and/or polyfunctional (meth)acrylic ester which hasbeen obtained by transesterification in the presence of anorganotitanium catalyst and from which the catalyst residue has not beenremoved.
 2. A composition according to claim 1, which is roomtemperature-stable and hot water-curable.
 3. A composition according toclaim 1, organotitanium wherein said catakyst comprises an alkyltitanate.
 4. A composition according to claim 3, wherein the alkyltitanate is tetra-isopropyl titanate or tetra-n-butyl titanate.
 5. Acomposition according to claim 1, which contains 50-1000 ppm of Ti.
 6. Acomposition according to claim 1, which comprises a hydroxyalkyl(meth)acrylate, a higher alkyl (meth)acrylate and a polyfunctional(meth)acrylate.
 7. A composition according to claim 6, wherein themonomers are in the proportions 25-65% hydroxyalkyl (meth)acrylate,15-70% higher alkyl (meth)acrylate and 5-20% polyfunctional(meth)acrylate.
 8. A composition according to claim 6 or 7, wherein thehydroxyalkyl (meth)acrylate is hydroxypropyl methacrylate, the higheralkyl (meth)acrylate is lauryl or tridecyl methacrylate and thepolyfunctional (meth)acrylate is triethylene glycol dimethacrylate ortrimethylol-propane trimethacrylate.
 9. A liquid (meth)acrylic esterimpregnant composition comprising a hydroxyalkyl (meth)acrylate, ahigher alkyl (meth)acrylate and a polyfunctional (meth)acrylate, atleast one of the higher alkyl or polyfunctional (meth)acrylic esterbeing a (meth)acrylic ester which has been obtained bytransesterification in the presence of an organotitanium catalyst andfrom which the catalyst residue has not been removed.
 10. A compositionaccording to claim 1 which comprises in parts by weight:

    ______________________________________                                        Hydroxypropyl methacrylate                                                                           65                                                     Lauryl methacrylate (inc.                                                                            15                                                     catalyst residue 600 ppm as Ti)                                               Triethylene glycol dimethacrylate                                                                    20                                                     Azobisisobutyronitrile 0.4                                                    Inhibitor (sterically hindered                                                                       0.15                                                   substituted phenol)                                                           Residual Ti in ppm (based on whole                                                                   90                                                     formulation)                                                                  ______________________________________                                    


11. A composition according to claim 1 which comprises in parts byweight:

    ______________________________________                                        Hydroxypropyl methacrylate                                                                           65                                                     Lauryl methacrylate (inc.                                                                            15                                                     catalyst residue 600 ppm as Ti)                                               Triethylene glycol dimethacrylate                                                                    20                                                     (inc. catalyst residue 1000 ppm as Ti)                                        Azobisisobutyronitrile 0.4                                                    Inhibitor (sterically hindered                                                                       0.15                                                   substituted phenol)                                                           Residual Ti in ppm (based on whole                                                                   290                                                    formulation)                                                                  ______________________________________                                    


12. A composition according to claim 1 which comprises in parts byweight:

    ______________________________________                                        Hydroxypropyl methacrylate                                                                        25                                                        Tridecyl methacrylate                                                                             70                                                        (including catalyst                                                           residue 150 ppm as Ti)                                                        Trimethylolpropane  5                                                         trimethacrylate                                                               Azobisisobutyronitrile                                                                            0.4                                                       Inhibitor (sterically                                                                             0.15                                                      hindered substituted                                                          phenol)                                                                       Residual Ti in ppm  105                                                       ______________________________________                                    


13. A composition according to claim 1 which comprises in parts byweight:

    ______________________________________                                        Hydroxypropyl methacrylate                                                                          25                                                      Tridecyl methacrylate (purified)                                                                    52.5                                                    Tridecyl methacrylate 17.5                                                    (including catalyst                                                           residue 150 ppm as Ti)                                                        Trimethylolpropane    5                                                       trimethacrylate                                                               Azobisisobutyronitrile                                                                              0.4                                                     Inhibitor (sterically 0.15                                                    hindered substituted phenol)                                                  Residual Ti in ppm    26                                                      ______________________________________                                    


14. A composition according to claim 1 which comprises in parts byweight:

    ______________________________________                                        Hydroxypropyl methacrylate                                                                          25                                                      Tridecyl methacrylate (purified)                                                                    35                                                      Tridecyl methacrylate 35                                                      (including catalyst                                                           residue 150 ppm as Ti)                                                        Trimethylolpropane    5                                                       trimethacrylate                                                               Azobisisobutyronitrile                                                                              0.4                                                     Inhibitor (sterically 0.15                                                    hindered substituted phenol)                                                  Residual Ti in ppm    52.5                                                    ______________________________________                                    


15. A composition according to claim 1 which comprises in parts byweight:

    ______________________________________                                        Hydroxypropyl methacrylate                                                                          25                                                      Tridecyl methacrylate (purified)                                                                    17.5                                                    Tridecyl methacrylate 52.5                                                    (including catalyst                                                           residue 150 ppm as Ti)                                                        Trimethylolpropane    5                                                       trimethacrylate                                                               Azobisisobutyronitrile                                                                              0.4                                                     Inhibitor (sterically 0.15                                                    hindered substituted phenol)                                                  Residual Ti in ppm    79                                                      ______________________________________                                    


16. A composition according to claim 1 wherein the higher alkyl(meth)acrylate comprises a C₁₀ -C₁₄ -alkyl (meth)acrylate.